Retaining Tab for Standing-Seam Trays on Wood or Wood-Derivative Carriers

ABSTRACT

In roof covering systems using zinc or zinc-alloy trays with standing-seam crimping, the use of tabs secured by two screws is well known. The invention particularly relates to a metal fastening tab for securing a standing-seam tray on a wood or wood-derivative carrier, which comprises a first surface ( 1 ) with a perforation ( 2 ) for receiving a screw for attachment onto the carrier, a second surface ( 3 ) generally perpendicular to said first surface and including a hook ( 4 ) for engaging with the ridge of the tray to be secured, the two surfaces defining an edge ( 5 ), characterised in that the first surface includes a single perforation ( 2 ) for receiving a single screw, and in that the centre ( 6 ) of said perforation ( 2 ) is not included in the mediator ( 7 ) of the edge ( 5 ) in order to reduce the force applied on the tab and on the tray by the torque induced when tightening said screw. Such a tab, with a single large-diameter screw, is easier and quicker to place than traditional tabs. The tab is specially designed to limit its own torsion and to avoid any buckling of the tray to be secured when tightening the single screw.

This invention relates to roofing systems, in particular systems employing trays made of zinc or a zinc alloy for standing-seam crimping.

Such trays are normally fastened to the roof support using fixed and sliding metal tabs. The function of the fixed tabs is to secure the standing-seam tray to the support, which normally is made of wood or wood derivative, by blocking the thermal expansion movements of the zinc. The sliding tabs are designed to take up the expansion movements of the zinc caused by temperature variations, while still securing the standing-seam tray to the support. The present invention relates to the fixed tabs.

Existing fixed tabs are for example represented in the rules of the art as described in France in the document DTU 40.41 (DTU standing for Document Technique Unifié) [Unified Technical Document]) entitled “Couverture par éléments métalliques en feuilles et longues feuilles en zinc” [Roofing with sheet-metal elements and long sheets made of zinc]”. These fastening tabs have two holes, with or without a surround, whether staggered or not, and are fastened using ribbed nails or wood screws 4 mm in diameter. They are normally installed along the joint, every 33 cm.

However, we have found that ribbed nails, and also small-diameter screws, smaller than 4 mm, may lift up because of wood drying cycles and repetitive wind forces. Also, many roofers use automatic nailers to save fitting time, which however creates greater difficulty in implementation because of the size of the machine. In addition, the nails are often struck hard and they deform the tabs, or are struck beside the holes in the tab, thereby running the risk of insufficient performance in terms of tear strength. A poorly installed tab creates a risk of poor cramping of the joint and therefore a lack of sealing and of attractiveness.

Although switching to a single large-diameter screw seems a priori to be advantageous, it does however pose a specific problem that has to be solved. Such a tab is mounted in fact by aligning it and attaching it along the tray to be fastened. However, when the single screw is tightened, a rotational torque is transmitted to the tab, this being greater the larger the diameter of the screw. Such screws are also very often provided, on their head, with lugs initially designed for countersinking and thus better penetrating the wood. These generate additional frictional forces which further increase the torque transmitted to the tab during tightening. This torque makes the tab pivot to the point that one of its ends bears on the tray to be fastened with a sufficient blocking force. It transpires that this blocking force may deform the tab and the tray, something which it is desired to avoid.

The subject of the present invention is a fastening tab using a single screw, and therefore simpler and quicker to fit than conventional tabs. This tab is especially designed to prevent it from being deformed and to prevent it deforming the tray to be fastened while the single screw is being tightened. The tab therefore provides greater security of implementation and better mechanical performance.

FIG. 1 illustrates the invention in a three-dimensional isometric view. FIG. 2 shows a tab seen from above.

The invention relates in particular to a metal fastening tab for securing a standing-seam tray on a support made of wood or wood derivative, comprising a first surface (1) provided with a perforation (2) for receiving a screw for fastening onto the support, a second surface (3) generally perpendicular to said first surface and including a hook (4) for engaging with the edge of the tray to be secured, these two surfaces defining a line of intersection (5) of length L, characterized in that said first surface has a single perforation (2) for receiving a single screw and in that the center (6) of said perforation (2) does not lie on the mid-perpendicular (7) to the line of intersection (5) so as to reduce the force felt on the tab and on the tray by the torque caused when said screw is being tightened.

This tab is more particularly characterized in that the center (6) of the perforation (2) lies off-center by a distance D greater than 10% of L in relation to the mid-perpendicular (7) to the line of intersection (5) so as to reduce the force felt on the tab and on the tray by the torque caused when said screw is being tightened.

The off-center distance may be adjusted according to the forces resulting from the tightening torque. These forces essentially vary according to the size of the screw heads used.

It will be understood that, to reduce the force felt on the tab and on the tray by the torque caused by tightening said screw, it is necessary to off-center the center (6) of the perforation (2) by shifting it away from the end (9) of the tab intended to reflect, onto the tray, the torque transmitted when the screw is being tightened, and not in the opposite direction. It is therefore clear that FIGS. 1 and 2 correspond to a part designed for a fastening screw with a right-handed thread, that is to say the usual case in which the tightening direction is clockwise. In the representation shown in FIG. 2, the perforation therefore has to be off-centered to the right.

It is useful to provide reinforcements (10) along the line of intersection (5). These also contribute to reducing the deformations of the tab during tightening, by blocking the angle formed by the surfaces (1) and (3).

The perforation (2) for receiving the fastening screw will preferably be provided with a surround (11), the opening angle of which is usefully greater than 100°.

This makes it possible to reduce the area of contact with the head of the screw and therefore to reduce the frictional forces and thereby also the torque transmitted to the tab during tightening. There are solutions for reducing friction by lubricating or by the use of interfacial materials, but these have the drawback of complicating the work of the operator and of increasing the cost of the solution.

It is preferred to use an AISI 304 stainless steel sheet to produce the part by stamping. A thickness of 0.4 mm is suitable.

The novel tab is fixed using a single screw of 5 mm or 6 mm diameter. Such a screw no longer lifts up under the effects of vibrations caused by the wind and by the dimensional variations of the supports. Its superior tear strength permits the tabs to be installed with a maximum spacing of 75 cm instead of the usual maximum spacing of 33 cm. The novel tab therefore significantly improves installation comfort, while at the same time making fitting easier and saving a significant amount of fitting time by the reduction in the number of tabs and the number of fastening operations. Moreover, these tabs are particularly compact, with no superfluous use of metal. 

1-6. (canceled)
 7. A metal fastening tab for securing a standing-seam tray on a support made of wood or wood derivative, comprising a first surface having a perforation configured to receive a screw for fastening onto the support, a second surface generally perpendicular to said first surface, the second surface including a hook configured to engage with an edge of the tray to be secured, the first surface and the second surface defining a line of intersection of length L, wherein the perforation of the first surface is a single perforation configured to receive a single screw and wherein the center of the perforation does not lie on the mid-perpendicular to the line of intersection, thereby reducing the force felt on the tab and on the tray by the torque caused when the screw is being tightened.
 8. The tab of claim 7, wherein the center of the perforation lies off-center by a distance D greater than 10% of L in relation to the mid-perpendicular to the line of intersection thereby reducing the force felt on the tab and on the tray by the torque caused when the screw is being tightened.
 9. The tab of claim 7, wherein reinforcements produced by stamping are provided along the line of intersection.
 10. The tab of claim 7, wherein the perforation for receiving the screw for fastening to the support is provided with a surround.
 11. The tab of claim 10, wherein said surround has an opening angle of greater than 100°.
 12. The tab of claim 7, produced by stamping a sheet of AISI 304 stainless steel. 